The global depletion of the non-renewable energy resources has rapidly increased in recent years. How to improve the energy efficiency has become a worldwide issue. In China, the energy-saving issue is much more prominent. According to a recent statistic, the total amount of LCD televisions being used in China exceeds 100 million, and will reach 3.4 billion in the next 58 years. By then, the annual power consumption of the televisions will exceed 50 billion kilowatt-hours (kWh) with ⅔ thereof being consumed by the displays. Since the LCD has become the most popular display medium in the world, the technical issues of reducing energy consumption of the LCD have become a worldwide important topic and task in the field of display technology.
Energy consumption of an LCD arises mainly from the backlight, the driving mode, the liquid crystal material and the peripheral components thereof. Among next-generation LCD technologies, the most attractive one is the blue phase liquid crystal display (BP-LCD) technology. The BP-LCD has the following four outstanding advantages over the conventional LCD technologies. First, the blue phase liquid crystal exhibits a fast response at microsecond level to an electric field, is applicable to a field sequential driving mode, and does not need a color filter. Second, the blue phase liquid crystal macroscopically exhibits optical isotropy, so that the alignment of the inner surface of a display substrate is no longer required. Third, the BP-LCDs can provide a relatively wide viewing performance and do not need any viewing angle compensation film. Fourth, the transmittance of the light from the backlights of the BP-LCDs is insensitive to the substrate gap, and thus the substrate gap does not need to be strictly controlled during the fabrication process. Such a feature of the BP-LCDs can greatly simplify the fabrication process and is useful for manufacturing large LCD panels.
As compared with a conventional LCD, a BP-LCD may reduce the backlight power consumption by about ⅓, the energy consumption during its fabrication may reduce by about 40%, and the cost of raw materials thereof may reduce by about 19%. Since the techniques and processes of manufacturing a BP-LCD are similar to that of the conventional LCD, they can be produced by the same manufacturing facilities. So, the key points of improving the BP-LCD technology reside in the development of blue phase liquid crystal (BPLC) materials.
In 2002, YANG Huai and Kikuchi, at al., reported a polymer-stabilized BPLC composite. Based on the composite, Samsung produced the first polymer-stabilized BP-LCD prototype in the world. The prototype was exhibited at the Display Week 2008 and aroused great repercussions in the display field. This polymer-stabilized BP-LCD can realize an image-driving speed of 240 Hz or greater, and thus can provide a naturally-appearing moving imagery. Therefore, the development of polymer-stabilized BPLCs is becoming the focus of the attentions in the art of manufacturing LCDs.
It is known that a polymer-dispersed liquid crystal is a composite formed by uniformly dispersing nematic liquid crystal droplets in a polymer matrix. Because the polymer-dispersed liquid crystal has excellent electro-optical properties and is easy to achieve large-scale production, it has been widely used in large-size flexible display devices, non-linear optical materials, electronically-controlled smart glass, liquid crystal gratings and so on. However, there are two main obstacles for manufacturing LCDs based on the polymer-stabilized BPLCs, including: (1) it is difficult to manufacture large panel with high uniformity using the polymer-stabilized BPLCs of wide temperature range; and (2) the microstructure of the polymer network is difficult to control precisely, and the life of the LCDs based on the polymer-stabilized BPLCs may be shortened significantly because the amount of the monomers used for polymerization is usually less than 10 wt % such that the resultant polymer network tends to deform under the effect of an applied electric field.
Therefore, in the field of LCDs, there is a great demand for the development of a useful BPLC, which can exhibit a wide temperature range, a lower driving voltage and a higher stability in electric field.